'\"
'\" Generated from file 'token\&.man' by tcllib/doctools with format 'nroff'
'\"
.TH "string::token" n 1 tcllib "Text and string utilities"
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.SH NAME
string::token \- Regex based iterative lexing
.SH SYNOPSIS
package require \fBTcl  8\&.5\fR
.sp
package require \fBstring::token  ?1?\fR
.sp
package require \fBfileutil \fR
.sp
\fB::string token text\fR \fIlex\fR \fIstring\fR
.sp
\fB::string token file\fR \fIlex\fR \fIpath\fR
.sp
\fB::string token chomp\fR \fIlex\fR \fIstartvar\fR \fIstring\fR \fIresultvar\fR
.sp
.BE
.SH DESCRIPTION
This package provides commands for regular expression based lexing
(tokenization) of strings\&.
.PP
The complete set of procedures is described below\&.
.TP
\fB::string token text\fR \fIlex\fR \fIstring\fR
This command takes an ordered dictionary \fIlex\fR mapping regular
expressions to labels, and tokenizes the \fIstring\fR according to
this dictionary\&.
.sp
The result of the command is a list of tokens, where each token
is a 3-element list of label, start- and end-index in the \fIstring\fR\&.
.sp
The command will throw an error if it is not able to tokenize
the whole string\&.
.TP
\fB::string token file\fR \fIlex\fR \fIpath\fR
This command is a convenience wrapper around
\fB::string token text\fR above, and \fBfileutil::cat\fR, enabling
the easy tokenization of whole files\&.
\fINote\fR that this command loads the file wholly into memory before
starting to process it\&.
.sp
If the file is too large for this mode of operation a command
directly based on \fB::string token chomp\fR below will be
necessary\&.
.TP
\fB::string token chomp\fR \fIlex\fR \fIstartvar\fR \fIstring\fR \fIresultvar\fR
This command is the work horse underlying \fB::string token text\fR
above\&. It is exposed to enable users to write their own lexers, which,
for example may apply different lexing dictionaries according to some
internal state, etc\&.
.sp
The command takes an ordered dictionary \fIlex\fR mapping
regular expressions to labels, a variable \fIstartvar\fR which
indicates where to start lexing in the input \fIstring\fR, and a
result variable \fIresultvar\fR to extend\&.
.sp
The result of the command is a tri-state numeric code
indicating one of
.RS
.TP
\fB0\fR
No token found\&.
.TP
\fB1\fR
Token found\&.
.TP
\fB2\fR
End of string reached\&.
.RE
.IP
Note that recognition of a token from \fIlex\fR is started at the
character index in \fIstartvar\fR\&.
.sp
If a token was recognized (status \fB1\fR) the command will
update the index in \fIstartvar\fR to point to the first character of
the \fIstring\fR past the recognized token, and it will further extend
the \fIresultvar\fR with a 3-element list containing the label
associated with the regular expression of the token, and the start-
and end-character-indices of the token in \fIstring\fR\&.
.sp
Neither \fIstartvar\fR nor \fIresultvar\fR will be updated if
no token is recognized at all\&.
.sp
Note that the regular expressions are applied (tested) in the
order they are specified in \fIlex\fR, and the first matching pattern
stops the process\&. Because of this it is recommended to specify the
patterns to lex with from the most specific to the most general\&.
.sp
Further note that all regex patterns are implicitly prefixed
with the constraint escape \fBA\fR to ensure that a match starts
exactly at the character index found in \fIstartvar\fR\&.
.PP
.SH "BUGS, IDEAS, FEEDBACK"
This document, and the package it describes, will undoubtedly contain
bugs and other problems\&.
Please report such in the category \fItextutil\fR of the
\fITcllib Trackers\fR [http://core\&.tcl\&.tk/tcllib/reportlist]\&.
Please also report any ideas for enhancements you may have for either
package and/or documentation\&.
.SH KEYWORDS
lexing, regex, string, tokenization
.SH CATEGORY
Text processing